Temperature dependence of the upper-branch polariton population in an organic semiconductor microcavity

We explore the distribution of polaritons along the upper polariton branch of a strongly coupled organic-semiconductor microcavity as a function of temperature following nonresonant optical excitation. Measurements of polariton emission from a high-finesse cavity containing a thin film of a J-aggregated cyanine dye were performed as a function of external detection angle and temperature and compared with the results of detailed numerical simulations. We show that a full description of temperature-dependent upper-branch polariton emission can only be obtained by accounting for the interplay between two mechanisms that populate polariton states, namely, thermally assisted exciton scattering and direct radiative pumping of the photonic component of polariton states via the radiative decay of weakly coupled "reservoir" excitons. Our measurements provide a full description of the basic mechanisms at play in an organic microcavity, and may help guide the development of organic polariton-based devices.